Unlike most kinds of renewable energy, wave power can produce power continuously. Ocean waves represent a considerable renewable energy resource. All of the energy is concentrated near the water surface with little wave action below 165 ft (50 meters) depth. This makes wave power a highly concentrated energy source with much smaller hourly and day-to-day variations. The rising and falling of the waves off shore can be captured by several devices specifically designed for this purpose.
Wave power is perhaps the least intrusive of all the renewable energy technologies. Wave power is very environmentally friendly. It does not create any waste, does not have any CO2 emissions or criteria pollutants, there is no noise pollution, no visual impact and it does not threaten marine life. Although the technology is limited to coastal locations its potential impact is large because of the large concentration of population along the coasts and the suitability of most coastal locations to the implementation of wave power. Proponents claim that the energy cost for producing electricity via wave power will be competitive with conventional power within a very short time.
However, wave power technology is still in its infancy with many competing technologies. The reliability of the devices for capturing energy from the waves has not been demonstrated on a very large scale. Some devices are quite complex and may require quite a bit of refinement before they can be considered mature technology. Wind power currently has the lowest cost of producing electricity of any of the renewable energy technologies and is the most successful technology, but it suffers from its intrusiveness, noise and danger to wildlife.
Wave power is located along the coasts of many areas of the world. This map shows the potential power that could be generated from waves expressed as kW/meter of wave front. Sites with an average wave power level of over 15 kW/m have the potential to generated wave energy at a competitive price.
Ocean Power Delivery Ltd manufactures a buoy to capture power from waves. OPD's Pelamis wave generation system uses a "smart," ocean-going buoy to capture and convert wave energy into a controlled mechanical force which drives an electrical generator. The buoy is a semi-submerged, articulated structure composed of cylindrical sections linked by hinged joints. The wave-induced motion of these joints is resisted by hydraulic rams, which pump high-pressure oil through hydraulic motors via smoothing accumulators. The hydraulic motors drive electrical generators to produce electricity. The 750kw full-scale prototype is 120m long and 3.5 m in diameter and will contain three power conversion modules, each rated at 250kW. The generated AC power is converted into high voltage DC and transmitted ashore via an underwater power cable. The Pelamis is enhanced with sensors which continuously monitor the performance of the various subsystems and surrounding ocean environment. In the event of very large oncoming waves, the system automatically disconnects. When the wave heights return to normal, the system reconnects and recommences energy conversion and transmission. Ideally the Pelamis would be moored in waters approximately 50-60m in depth, 5-10km from the shore.
OPD has received a contract to build the first three modules of a wave farm to be built off the coast of Portugal. The three modules will generate 2.25 MW of power. They have a letter of intent to install another 30 machines upon satisfactory completion of the first phase.
Ocean Power Technologies (OPT) PowerBuoy™ is an offshore wave energy converter which is submerged more than a meter below the water's surface. Inside, a piston-like structure moves as the PowerBuoy™ bobs with the rise and fall of the waves. This movement drives a generator on the ocean floor, producing electricity, which is sent to the shore by an underwater cable. The buoy is designed to be deployed in approximately 100 feet (30 meters) of water. The buoy is mounted on the sea bottom using a proprietary anchoring system that avoids any damage or threat to the sea bed or sea life. An OPT "power plant" will consist of an array of identical PowerBuoys™ that are electrically connected to provide the desired power capacity. A power plant will have a a matrix of buoys with masts that rise above the surface of the water, with navigational aids attached, such as a radar reflector, day mark, and warning light to help aid mariners in the vicinity.
The total operating cost of generating power from an OPT wave power station is projected to be only (US) 3-4¢/ kWh for 100 MW systems and (US) 7-10¢/kWh for 1 MW plants, including maintenance and operating expenses, as well as the amortized capital cost of the equipment.
OPT has several projects which will demonstrate its technology. The companies first semi-commercial buoy has been installed for the U.S. Navy in Hawaii in a facility which will eventually generate up to 1 MWe. The first buoy, with a capacity of 40 to 50 kW, has been installed. Its largest project is providing a power generating facility for the Spanish utility Iberdrola to build a system off the coast of Spain consisting of 10 buoys that will generate 1.25 MWe. More recently it has signed an agreement with Iberdrola to identify suitable sites along the French coastline. In the second phase of this project a wave power station of 2 to 5 MW will be installed. it It also has a contract with Lockheed Martin to develop a smaller version of its buoy to power self-sufficient sensors used in defense and security systems. The prototype version of this buoy has been delivered and tested in the ocean and has successfully demonstrated performance according to design specifications. It has been awarded a second phase program to design and planing for the production of system development of production quantities of the small-scale buoy system. It also has an agreement with the New Jersey Board of Public Utilities to install and operate one of its systems off the coast of New Jersey.
Wavegen's device is called the Limpet (Land Installed Marine Powered Energy Transformer). It is a near-shore wave-powered station that uses an oscillating water column (OWC) to generate power. By largely being installed on land it avoids the maintenance problems that might be encountered with a sea mounted buoy. In a development unit that has been in operation at Islay for over a year, performance has been optimized for annual average wave intensities of between 15 and 25kW/m. The water column feeds a pair of counter-rotating turbines, each of which drives a 250kW generator, giving a nameplate rating of 500kW. Siemens Hydro purchased Wavegen on 5/24/05.
WAVEenergy is a wave energy converter based on the overtoping principle, called the Seawave Slot-Cone Generator (SSG), that uses reservoirs placed on top of each other, in which the potential energy of the incoming wave will be stored. Water is captured in the top reservoir and then runs through the lower reservoirs to a multi-stage turbine for electric power production. Using multiple reservoirs results in a high overall efficiency. The converter can be adapted for onshore, breakwater or offshore installations. A pilot project is to be installed on the Island of Kvitsøy in December of 2005 to demonstrate, at full-scale, the operation of one module of the SSG wave energy converter in an 19 kW/m wave climate, including turbine, generator and control system.
Seapower Pacific (acquired in February 2005 by Renewable Energy Holdings) an Australian company, has designed and built the CETO wave energy converter. The converter is mounted permanently on the ocean floor. CETO is basically a steel box that sits on the sea bed and pumps high pressure seawater to the shore, where it can be used either to produce fresh water via reverse osmosis or to drive turbines for power generation.
As waves move over the top of the unit, their energy is converted into a pressure which presses down on a disc that transmits the force to reciprocating pumps inside the box, which deliver pressurized water to the shore. The converter box measures about 20 meters by 4.5 meters and is capable of pumping water at a pressure of 1,000 psi. Each unit is designed to produce about 100 kW of power. The trial unit was sunk close to the shore in just 7m (23ft) of water for the testing process, and has an access tower that rises above the surface of the sea. Commercial units would be located further off the coast, in deeper water and will not have the access tower. The CETO device prototype, which has been undergoing testing since March 2005 has, in initial testing, successfully transmitted high pressure seawater to shore at in excess of 500 psi. This pressure, is lower than the 1000 psi expected in commercial units because of the boxes low submergence, is within the design parameters required to generate electricity on-shore using conventional hydro electric power turbines. The device is designed to be normally installed at a submergence of 10 to 20 meters within 1 km of shore.
The Wave Power Group at the University of Edinburgh has a long list of links to various wave power websites.
Ocean Power Delivery Ltd (OPD), Edinburgh, Scotland
Ocean Power Technologies, Inc., Pennington, New Jersey
Wavegen, Inverness, Scotland
WAVEenergy, Aalgard, Norway
Renewable Energy Holdings PLC, (owner of Seapower Pacific, developers of CETO), England